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BioMed Research International
Volume 2014, Article ID 809736, 9 pages
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Research Article
Evaluation of Drought Tolerance of the Vietnamese Soybean
Cultivars Provides Potential Resources for Soybean Production
and Genetic Engineering
Nguyen Binh Anh Thu,1 Quang Thien Nguyen,1 Xuan Lan Thi Hoang,1
Nguyen Phuong Thao,1 and Lam-Son Phan Tran2
1

School of Biotechnology, International University, Vietnam National University HCMC, Quarter 6, Linh Trung Ward,
Thu Duc District, Ho Chi Minh City 70000, Vietnam
2
Signaling Pathway Research Unit, RIKEN Center for Sustainable Resource Science, 1-7-22 Suehiro-cho, Tsurumi,
Yokohama 230-0045, Japan
Correspondence should be addressed to Nguyen Phuong Thao; and Lam-Son Phan Tran;
Received 6 February 2014; Revised 28 February 2014; Accepted 3 March 2014; Published 7 April 2014
Academic Editor: Alberto Reis
Copyright © 2014 Nguyen Binh Anh Thu et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
Drought is one of the greatest constraints to soybean production in many countries, including Vietnam. Although a wide variety of
the newly produced cultivars have been produced recently in Vietnam through classical breeding to cope with water shortage, little
knowledge of their molecular and physiological responses to drought has been discovered. This study was conducted to quickly
evaluate drought tolerance of thirteen local soybean cultivars for selection of the best drought-tolerant cultivars for further field
test. Differences in drought tolerance of cultivars were assessed by root and shoot lengths, relative water content, and droughttolerant index under both normal and drought conditions. Our data demonstrated that DT51 is the strongest drought-tolerant
genotype among all the tested cultivars, while the highest drought-sensitive phenotype was observed with MTD720. Thus, DT51
could be subjected to further yield tests in the field prior to suggesting it for use in production. Due to their contrasting droughttolerant phenotypes, DT51 and MTD720 provide excellent genetic resources for further studies underlying mechanisms regulating
drought responses and gene discovery. Our results provide vital information to support the effort of molecular breeding and genetic



2
has to import 2.5 million tons of soybean [6]. As a result,
development of soybean elite cultivars, which can sufficiently
cope with water scarcity, has been an important task for
soybean research community in Vietnam [14]. Thanks to
soybean breeder’s efforts, many soybean hybrid cultivars with
improved productivity under drought have been recently
developed by different research institutions and applied
across the country [6].
A number of assessment methods have been exploited
to quickly examine drought tolerance ability of soybean
cultivars under stressed and nonstressed conditions based on
their root and shoot growth rates [15]. It is well established
that root length is one of the primary traits that support
plants to tolerate the limited water conditions [16]. Thus,
analyzing dynamics of root growth under severe drought
conditions is important to specify the contribution of roots
to drought adaptation [17]. In soybean, roots are distributed
in the top soil when water is sufficient, but under water deficit,
extensive root growth and development occurs deeper in the
soil profile [17, 18]. Early establishment of the root system
(seedling vigor) could be one of the important traits in the
selection of soybean genotypes for improvement of soybean
production in drought-prone areas [12]. Shoot growth rate of
soybean is reduced by drought during vegetative growth and
early reproductive development. However, soybean plants
with strong drought-tolerant ability can be recovered after
rewatering for certain days [19]. It has been reported that

2. Materials and Methods
2.1. Plant Materials. In this study, 13 Vietnamese soybean
cultivars collected from Can Tho University (MTD176,
MTD720, MTD751, MTD765, MTD772, MTD775-2, and
MTD777-2) and Vietnam Legumes Research and Development Center (DT20, DT22, DT26, DT51, DT84, and DT96)
were used along with the reference phenotype W82.
2.2. Net House Conditions and Cultivation Techniques. All
plants in the present study were cultivated inside a net house
that helped to maintain a consistent temperature range (28–
30∘ C) and a relative humidity (60–70%), together with a
photoperiod of 12 h light and 12 h dark conditions. Initially,
one seed was sown at 2 cm depth in each plastic tube with
parameters specified below which was filled with a premixed
standard potting soil. Irrigation was thoroughly undertaken
every single day to ensure the distribution of identical water
amount for individual plant.
2.3. Examination of Root and Shoot Growth at Seedling and
V3 Stages under Well-Watered Conditions. Two screening
methods using two different tube systems described in [24]
were applied to examine physical growth of plants at certain
stages under well-watered conditions. For seedling stage
assessment, 30 plastic tubes (40 cm in height and 6.5 cm in
diameter) were adhered to a tray representing each cultivar.
After 12 days of planting, each tube was cut longitudinally in
order to safely isolate the whole root system from potting soil.
On the other hand, the V3-stage assessment (21 days after
sowing) was implemented with also 30 plastic tubes (80 cm
in height, 10 cm in upper diameter, and 6.5 cm in bottom
diameter)/cultivar.
2.4. Drought-Induced Treatments. Sixty 4-day-old seedlings/


DT84

b

(b)

0.9

0.25

bcd
cde cde
de de de

0.1

abcd
bcde
bcde

abc

ab ab

e
ab abcd
abc ab abcd a abcd
0.05 bcd abcd abc
bcd bcd cd

ab
ab
d ad
ab
ab ab
ab ab ab ab
ab
b

0.1
DT84

MTD777-2

DT26

DT22

MTD765

DT20

MTD751

MTD176

DT96

MTD772


Williams 82

(c)

MTD775-2

0

0

Williams 82

Root dry matter (g)

0.8
a

0.2
0.15

DT51

Williams 82

DT51

DT84

DT26


fg

MTD176

fg efg

MTD772

ef fg

a
d

DT96

g fg

b

c

cd bc
cd cd cd cd
de
de
de
ef f de
b b cde cde bcd a de bc
e
e


gh fgh fg

Shoot length (cm)

cd

DT22

50

b

c

cd

DT96

Taproot length (cm)

60

50
45
40
35
30
25
20

] × 100.
(TW − DW)

(1)

Drought-tolerant index (DTI) was calculated as described
in [25]. Five seeds of each variety were geminated separately
in each of the 5 plastic tubes (25 cm in height and 30 cm
in diameter) (𝑛 = 25). The plants were maintained under
well-watered conditions in net house. For drought treatment,
water was withheld from 12-day-old plants for 15 days. The
percentage of nonwithered plants was determined after 1,
3, 5, 7, 9, 11, 13, and 15 days after water withholding. After
drought treatment, the plants were reirrigated for 15 days. The
percentage of recovered plants was identified after 1, 3, 5, 7, 9,
11, 13, and 15 days of reirrigation. The drought-tolerant index

of soybean varieties (referred to as a surface of a radar chart,
comprised of multiple axes) was calculated as
DTI =

1
sin 𝛼 (𝐷1 𝑅1 + 𝑅1 𝐷3 + 𝐷3 𝑅3 + 𝑅3 𝐷5 + 𝐷5 𝑅5
2

(2)

+𝑅5 𝐷7 + ⋅ ⋅ ⋅ + 𝐷15 𝑅15 + 𝑅15 𝐷1 ) ,
where 𝐷𝑛 is the percentage of nonwithered plants after 𝑛
day(s) of drought treatment, 𝑅𝑛 is the percentage of recovered

60
50
40
30
20
10

55

DT84

DT51

DT20

DT26

DT22

DT96

MTD772

MTD775-2

MTD176

MTD751

MTD777-2

MTD772

MTD775-2

MTD176

MTD751

MTD765

MTD777-2

MTD720

Williams 82

0

20th day
25th day

(a)

(b)

Relative water content (%)

90
a
80

MTD775-2

MTD772

MTD176

MTD751

MTD777-2

MTD720

MTD765

Williams 82

60

(c)

Figure 2: Examination of RWC of 13 soybean cultivars and the reference cultivar W82. For drought treatment, water withholding was applied
to 12-day-old plants for 15 days. SMC was recorded in each pot of each cultivar at 5-day intervals during the measurement of RWC of
the soybean cultivars. (a) SMC was measured under well-watered condition. (b) SMC was measured under drought condition. Error bars
represent standard error (𝑛 = 3). (c) RWC under normal (black bars) and drought conditions (grey bars). Error bars represent standard error
(𝑛 = 15). Different letters indicate significant difference within a treatment according to Duncan’s test (𝑃 < 0.05 level).

were shown on the figures, and error bars represent the
standard errors.

3. Results and Discussion


70.0

Drought-tolerant index (×104 )

70
60
50
40
30
20
10

60.0
50.0
40.0
30.0
20.0
10.0
DT51

DT84

DT26

DT22

MTD765

DT96


MTD176

MTD751

MTD775-2

MTD777-2

MTD720

5th day
10th day
15th day
20th day

MTD777-2

0.0

0

MTD720

Soil moisture content (%)

BioMed Research International

25th day
30th day

and MTD777-2 had medium taproot length (40–50 cm).
The remaining varieties, including MTD775-2, MTD176, and
MTD720, showed short taproot length (35 cm) that also includes DT84
and MTD765. A number of cultivars, such as DT20, MTD751,
MTD176, MTD772, and DT96, exhibited medium shoot
length (30–35 cm), while MTD720, MTD775-2, DT26, DT22,

and W82 fell into the low shoot length category (0.045 g). DT20, DT51,
DT26, MTD751, DT84, and MTD176 had medium root
DM (from 0.035 to 0.045 g), while W82, MTD772, DT96,
MTD765, and MTD775-2 showed low root DM (0.15 g). DT22, DT20, W82, MTD765, DT96,
and MTD772 exhibited medium root DM (0.09–0.15 g),
whereas MTD751, MTD720, DT51, MTD176, and MTD775-2


20th day
25th day
(a)

DT51

DT84

DT26

DT22

DT20

DT51

DT84

MTD772

MTD777-2

MTD176

DT20

a

1.2

a
bc

cd
g

f

f

MTD751

0.6

i

MTD772

0.8

g

DT22

1

DT96

f


MTD777-2

DT22

DT51

MTD765

DT26

MTD775-2

DT20

MTD176

MTD751

MTD772

DT84

DT96

MTD720

b

(d)


DT96

Williams 82

DT51

DT26

DT84

DT22

MTD765

DT20

DT96

MTD176

MTD775-2

MTD720

MTD777-2

MTD751

MTD772


a
a
fg
ab bcd abc cd de
cde
30 g
cde bcd
ef f f
25 g
20
15
10
5
0
MTD720

ab a
de cd bcd abca abca a a
e
e
b
bc b
60 fgb gcd fg f b f
cd
e de
e
50

Shoot length (cm)



MTD751

MTD176

DT51

DT84

DT26

DT22

DT20

DT96

MTD777-2

5th day
10th day
15th day

Williams 82

MTD772

MTD775-2

MTD765

DT51

DT20

MTD176

MTD720
MTD775-2

Drought condition

MTD777-2

DT51

DT26

DT84

DT22

MTD765

DT96

DT20
(a)

Williams 82
MTD772

DM. A similar result was observed in previous study of
Manavalan et al. [24]. This might be explained by the fact
that, although a decrease of total DM may be due to growing
conditions, the distribution of biomass may also result from
change in resource pools, leaf senescence, the reduction in
photosynthesis and cell division, and the change in cell wall
composition [16, 26, 27].
3.3. RWC under Normal and Drought Conditions. Evaluation
of RWC of various plants, especially under drought, will
provide information about their tolerance levels in response
to stress conditions [28]. This value highlights potential
cultivars with better tolerance and thus higher yield, which
exhibit higher RWC under drought. Thus, to further examine
the contrasting drought responsive phenotypes of DT51 and
MTD720, we determined the RWC of these two cultivars
together with other local soybean cultivars and W82 during
both normal and drought conditions. The SMC was monitored during drought treatment to ensure the similar SMC
levels among different pots (Figures 2(a) and 2(b)). As a
result, under both normal and drought conditions, DT51
showed the highest RWC (83.74% and 81.07%, resp.), and
MTD720 displayed the lowest RWC (74.14% and 73.07%,
resp.) (Figure 2(c)). These results suggested that DT51 and
MTD720 are the highest and lowest drought-tolerant cultivars, respectively.
3.4. DTI under Normal and Drought Conditions. As a means
to evaluate more exactly drought-tolerant capacity of the
tested 13 soybean cultivars, we examined the DTI that
represents survival and recovery rates of plants after drought
treatment. This method was shown to be useful and timesaving by [25] in evaluating the drought-tolerant capacity in
rice. Mau et al. (2010) also performed this method to compare


drought (49.5 cm) (Figure 4(c)). We observed that the shoot
length was more significantly inhibited than the root length
by stress (Figures 4(d) and 5), which was also supported
by a previous study [30]. DT51 exhibited the highest shoot
length under both normal and drought conditions (44.6
and 30.3 cm, resp.) (Figure 4(d)), and interestingly also had
the highest decrease of shoot length during stress when


8
compared with its respective one obtained under normal conditions. It is important to note that, in plants, the inhibition of
shoot length was a primary response to water deficit, which
might extend the period of soil water availability and plant
survival as an adaptive response [32]. On the other hand,
MTD720 exhibited short shoot length under both normal and
drought conditions (30.22 and 25.66 cm, resp.) (Figure 4(d)).
In addition, we also investigated the effects of drought
on root and shoot DMs. We found that all of the cultivars
showed decrease in root and shoot DMs under stress (Figures
4(e) and 4(f)). However, again, we did not observe a clear
correlation between the root length and the root DM, as well
as the shoot length and the shoot DM, suggesting that the DM
data might not be used as an important feature for evaluation
of drought tolerance. Published literature also suggests that
plant biomass should not be regarded as a sensitive parameter,
because the decrease in biomass accumulation is mainly
affected by long-term stress conditions [33].
Taken together, we recorded DT51 and MTD720 as
two cultivars having contrasting drought-tolerant features,
of which DT51 was the highest drought-tolerant cultivar,

Conflict of Interests
The authors declare that there is no conflict of interests
regarding the publication of this paper.

BioMed Research International

Acknowledgments
The authors would like to thank Dr. Tran Thi Truong from
Vietnam Legumes Research and Development Center and Dr.
Nguyen Phuoc Dang from Can Tho University for providing
seeds of various soybean cultivars. This work was funded by
Vietnam National Foundation for Science and Technology
Development (NAFOSTED) under Grant no. 106.16-2011.37
to Nguyen Phuong Thao.

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